The dependence of the melting temperature of the (dA)n.(dT)n double helix upon salt concentration has been examined in terms of two theoretical models. The first, a wholly thermodynamic model, shows that interaction of the salt component with helical and coiled forms of DNA must both be included to successfully account for our observations, but, the magnitudes of these apparent binding constants are 100-fold too large. Modification of the binding constant to take into account the high electrostatic potential near the charged polymeric chains leads to reasonable values for the binding constants. All-atom computer simulations predict the requisite electrostatic potentials of 4-5 kT near the phosphate groups of DNA, however, the extremely steep potential gradient requires knowledge of the locus of binding to within several tenths of an Angstrom unit. The dependence of the melting temperature of DNA upon salt concentration may alternatively be expressed in terms of the Donnan membrane equilibrium salt distribution parameter. The value of this parameter can be calculated from solutions of the Poisson-Boltzmann equation which give the electrostatic potential as a function of distance from the axis of an impenetrable cylinder of assumed charge separation and radius. Granting that a solution for the DNA helix is possible by virtue of its known geometry, it remains only to account for the salt distribution parameter of the denatured coiled form. This can be done using alternative choices of reasonable parameter values showing that a unique solution is not possible for the coiled form. Thus, the description of any coiling polyelectrolyte is indeterminate as a consequence of our lack of knowledge about the appropriate charge spacing and cylinder radius. Both models fit the observed dependence of the melting temperature of DNA upon salt concentration perfectly, however both models remain only qualitative, their limitations arising from our inability to specify distances at sub-Angstrom resolution. - nuceic acids, DNA, double helicies, triple helicies,calorimetry,thermodynamics, homopolynucleotides